The present invention relates generally to a chip for retaining optical fibers in registry with a lenslet and a process for fabrication of the chip, and more specifically to a process which uses fiber-retaining channels in the chip as an exposure mask for the creation of the lenslet.
Optical data communication networks utilize a large number of optical fibers which need to be accurately aligned with other system components to effect efficient coupling between the fibers and the system components. Similarly, fiber optic imaging systems make use of a plurality of optical fibers having inputs that need to be aligned and coupled, i.e. spaced at proper conjugates to the object and image planes
The coupling of optical signals from the fibers of both data communication networks and imaging systems benefits from fiber optic chips that include lenslets disposed near the endface of the fibers. Such lenslets focus and direct the light emitted or received by the fibers.
However, the use of lenslets creates additional degrees of freedom which must be controlled during the manufacturing process of the fiber optic chip. In particular, it is important to align the lenslet to the optical axis of the fiber, which may be accomplished by aligning the lenslet to a fiber-retaining channel that holds the optical fiber within the chip.
With conventional photolithographic processes, the alignment of the lenslet to a fiber-retaining channel requires additional processing steps in which an exposure mask must be separately registered to the fiber-retaining channel to define the location of the lenslet to be formed. Using an exposure mask in this manner introduces additional processing variables that must be controlled. As a result, the cost of the manufacturing process ultimately increases while the accuracy with which the lenslet location may be determined potentially decreases. A need therefore remains for a manufacturing process for creating a fiber array having lenslets registered to respective optical fibers, which utilizes fewer processing steps. In particular, it would be desirable to provide a process which effects registry between a lenslet and its respective fiber-retaining channel as the lenslet is formed.
In accordance with the present invention, a fiber optic chip having one or more fiber-retaining channels and a respective number of lenslets disposed in registry with the channels is provided. In addition, a process is provided for creating the fiber optic chip, where the process utilizes the channels as an exposure mask to define the locations of the lenslets. The use of the channels as an exposure mask ensures that the lenslets are accurately registered relative to the respective channels.
The fiber optic chip includes a substrate having a first surface and an etch stop layer disposed proximate the first surface of the substrate. A fiber retaining channel is disposed within the substrate. The fiber channel has an end disposed proximate the first surface of the substrate and has a longitudinal axis extending along the channel. A lenslet is disposed on the etch stop layer and has an optical axis substantially aligned with the longitudinal axis of the channel. The fiber optic chip may optionally include an alignment feature in the substrate.
The process includes a step of providing a masking layer, which includes a mask aperture, on a first surface of a substrate to mark the intended location of a fiber channel. A portion of the substrate located within the mask aperture is selectively removed to create the fiber channel. In addition, a processing material layer is provided on a second surface of the substrate opposite the first surface of the substrate. The processing material is exposed with light of a selected wavelength which is transmitted through the fiber channel to create an exposed region in the processing material layer. In this manner, the fiber channel functions as a mask, ensuring that the exposed region of the processing material layer is in registry with the fiber channel. Next the unexposed portion of the processing material layer is selectively removed to create a lenslet preform which is positioned in registry with the fiber channel. The lenslet preform is then processed, for example by heating, to impart a lenticular shape to the preform, thereby creating a lenslet in registry with the fiber channel.
Optionally, the masking layer may include an alignment feature aperture for the purpose of defining the location of an optional alignment feature. The optional alignment feature is formed by selectively removing a portion of the substrate located within the alignment layer aperture. For example, the alignment feature may be formed by an anisotropic etching process to create an alignment feature having a sidewall which is inclined with respect to the first surface of the substrate.
Additionally, the step of providing the processing material layer may optionally comprise providing one or more additional layers. A first such variation of the process comprises providing an optional etch stop layer adjacent the second surface of the substrate and providing a photosensitive lenslet-forming layer adjacent the etch stop layer. The etch stop layer is provided so that the substrate removal step may extend to the depth of the second surface of the substrate. Such a fiber channel extends from the first surface of the substrate to the second surface of the substrate. The photosensitive lenslet-forming layer may be further processed to create a lenslet, in a manner similar to that described above.
A second variation of the process comprises providing a processing material layer having an etch stop layer adjacent the second surface of the substrate, a lenslet-forming layer adjacent the etch stop layer, and a photo-sensitive layer adjacent the lenslet-forming layer. This three-layer configuration, which includes a separate photo-sensitive layer, permits the use of the lenslet-forming layer which is not photosensitive. The photo-sensitive layer is then exposed with light of a selected wavelength through the fiber channel to create an exposed region of the photo-sensitive layer. The process further comprises the step of removing the unexposed region of the photo sensitive layer to provide a lenslet mask comprising the exposed region of the light-sensitive layer. In turn, creation of the lenslet preform includes the step of selectively removing a portion of the lenslet forming layer not protected by the lenslet mask. Subsequent the formation of the lenslet preform, the lenslet mask may be removed from the lenslet preform, prior to creation of a lenslet from the lenslet preform. A third variation of the process is also provided and is substantially the same as the second variation but omits the etch stop layer. In this third case, the lenslet-forming layer is disposed adjacent the second surface of the substrate.